Saturday 3 July 2010 19.06 EDT
First published on Saturday 3 July 2010 19.06 EDT

The faces staring out from the prints covering the wall of a tiny museum in Tokyo are uniformly podgy. They are the yokozuna, men who, over the centuries, have reached the apex of the ancient sport of sumo wrestling. Possessed of devastating strength and skill, they are also feted for modesty in victory and dignity in defeat.

The coach parties of pensioners at the sumo museum in Tokyo's Ryogoku district linger before the yokozuna (grand champions), laughing as they recognise faces from the past and, perhaps, hoping for happier times for Japan's de facto national sport.

However, the storm clouds are gathering above sumo, a 2,000-year-old sport celebrated in Japanese mythology, watched by warlords and emperors, and steeped in Shinto ritual and pretensions of moral rectitude.

The Japan Sumo Association (JSA) is today poised to suspend more than two dozen wrestlers – about a third of the top division – and coaches implicated in an illegal gambling ring that has shaken the once unimpeachable sport to its core. The talk is of tens of thousands of dollars in illicit bets, extortion, shady middlemen… and speculation about sumo's very future.

The JSA is expected to expel Kotomitsuki, an ozeki (champion) who has admitted placing large sums on baseball matches, a violation of Japan's strict gambling laws. Otake, a former wrestler-turned-sumo stable master, also faces expulsion. According to Japanese media, as many as 65 of 700 wrestlers have admitted betting illegally on baseball, cards, golf and mahjong.

In a crisis meeting last week the association stopped short of cancelling this month's 15-day tournament in Nagoya – one of only six Grand Sumo contests held each year – but NHK, the national broadcaster, may refuse to screen the bouts if it decides the governing body has failed take tough enough action.

It has received more than 8,000 protests from angry fans, almost two-thirds of whom say the tournament should not go on air for the first time in broadcasting history.

Large numbers of tickets remain unsold, and the food producer Nagatanien, the tournament's biggest corporate supporter, has withdrawn ¥12m (£90,000) in sponsorship money. Other sponsors are certain to follow.

But most damaging of ll is the exposure of sumo's ties with organised crime, a badly kept secret among insiders and long overlooked by the sumo hierarchy and the sport's administrators at the education ministry.

In the first of what is expected to be a string of arrests over illegal gambling, Mitsutomo Furuichi, a former wrestler and gang member, is suspected of attempting to extort more than ¥100m from Kotomitsuki in return for keeping quiet about his gambling habit.

Kotomitsuki, the highest ranked Japanese wrestler, admitted paying Furuichi ¥3.5m out of fear for his safety and that of his family.

In May, reports surfaced that coveted ringside tickets usually reserved for fan club members and corporate sponsors had found their way into the hands of senior figures in the Yamaguchi-gumi, Japan's most powerful crime syndicate.

The gang bosses had apparently wanted to appear on television to show solidarity with incarcerated gangsters (yakuza) watching live coverage of the bouts from their cells.

Jake Adelstein, author of Tokyo Vice and an authority on organised crime in Japan, said the scandal was connected with a fresh crackdown on a notoriously violent faction within the Yamaguchi-gumi that also had strong ties to the sumo world. "The media haven't suddenly decided to expose the relationship between sumo and the yakuza," Adelstein said. "The details were leaked to them by the police.

"Failed sumo wrestlers often end up as yakuza enforcers. The sumo world and the yakuza world have long been intertwined. Some ex-sumo wrestlers have even become yakuza bosses."

The media have united to condemn the failure of sumo's guardians to safeguard its morals, and called for a purge of anyone tainted by association with the scandal. "The [JSA's] leadership is as good as dead," the Asahi Shimbun said before calling on the body's entire 120-member board to resign in disgrace. The Yomiuri Shimbun, Japan's biggest-selling newspaper, said the JSA had "forfeited the public's trust".

The biggest scandal in sumo's modern history has come at just the wrong time for a sport still reeling from a flurry of incidents that have come close to destroying its reputation. Last December, a coach was sentenced to six years in prison in connection with the death of a 17-year-old trainee from his stable in 2007. The teenager died following an assault by three stable mates, one armed with a baseball bat, after he tried to abscond. His corpse was dotted with cigarette burns.

The death prompted calls for the authorities to address widespread bullying in sumo stables, where wrestlers train, eat and sleep together under the tutelage of their masters. Former wrestlers are supposed to imbue their charges with ethical values, as well as teaching them how to wrestle. In February, Asashoryu, a former grand champion who had dominated the sport in recent years, was forced to retire after breaking a man's nose in a drunken brawl outside a Tokyo nightclub. This came soon after several wrestlers had been expelled for possession of marijuana.

But some experts say sumo is being unfairly singled out for misdemeanours that barely raise an eyebrow in other sectors of Japanese society. "It has been open season on sumo for the past three years," said sumo writer Mark Buckton. "People do hold sumo wrestlers to higher standards of behaviour, but they have to admit that wrestlers are only doing what many other Japanese have been doing for years. Other sportsmen have been found guilty of illegal gambling, but no one said a word."

Sumo's current woes lie in its failure to adapt to the public and commercial demands of the modern age. After decades of insularity, the sport now attracts a global audience, and its elite ranks are filled with foreign wrestlers who are proving more successful than their Japanese counterparts.

Fewer athletic teenagers, particularly those from its traditional heartland in the rural north, feel the lure of sumo, with its spartan stable lifestyle and relatively poor salaries for all but those at the sport's pinnacle.

But Buckton dismissed the idea that the betting scandal was a symptom of a sport in terminable decline: "That's just not going to happen. Sumo is too much a part of the Japanese national psyche. At the moment, it is struggling to live in the modern world, that's all."